The present invention relates to a two-cannula syringe for the aspiration and injection of medicaments in the form of liquids.
Hypodermic syringes with a removable and thus also exchangeable cannula are known, inter alia from Swiss Pat. Nos. 590,661 and 639,856 as well as from European Patent Application, Publication No. 0,047,442.
Syringes for the self-injection of insulin solutions are described, inter alia, in European Patent Application, Publication No. 0,045,367. Reference is indeed generally made, in this European patent application, to the risks of contamination which arise in such applications (page 3), but there is no specific reference to the fact that it is the cannula which--above all in the case of repeated use--shows the greatest probability of contamination and thus represents the greatest risk of infection.
Working with throw-away hypodermic syringes also brings only an inadequate reduction of the risk of contamination: it is the place of puncturing, used over a relatively long period of time, of the medicine phial which primarily enters into consideration in connection with the transfer of germs to the cannula.
Even the exchange of the cannula between aspiration and injection can indeed lead to contamination, above all when the solution remains uncovered in the syringe during exchange or when such exchange requires contact with the cannula.
A double-cannula extraction device for sterile applications is described and claimed in European Patent Application, Publication No. 0,085,957. A puncturable double-cannula is represented specifically in the devices according to FIGS. 5 and 9 of this application, in which devices the two cannulae are designed to be located adjacent to one another and are also inserted together into the solution container. Through one of the cannulae liquid is extracted, and through the other air is introduced into the container under sterile conditions, for the purpose of pressure compensation.
Operating with one cannula for aspiration or filling and for injection does, moreover, conceal the danger of damage of the cannula, which can have a negative effect in the course of injection.
West German Pat. No. 378,629 teaches and claims a medicinal syringe, over the cannula of which--after introduction of the same into the blood vessel--a protective tube with blunt edges and without a tip can be pressed, in order in this manner to protect the interior of the blood vessel from the tip of the cannula. By definition, the protective tube cannot be used as an extraction or aspiration tube for liquid medicaments.
Finally, in German Utility Model No. 1,678,482, a small protective tube is described, which in the course of filling the syringe, for the purpose of the mechanical protection of the injection cannula, is placed on the latter. As is clearly evident, the small protective tube is conceived for a multiplicity of syringes; this clearly contradicts the most important aim of the two-cannula syringe of the invention, namely the minimization of contamination. In addition to this, before the syringe is used it is uncovered.
Only by means of the two-cannula syringe according to the invention described here, however, is the problem of exchange-free changing of cannulae between aspiration and injection fundamentally recognized and solved.